ENEMIES AND THEIR INFLUENCE. 



417 



Chapter XII., page 355.) Mr. Simon also attributes this use of the tube 

 to the ants of northern Africa, particularly to Dolichoscaptus vittatus, 

 which drives into the earth a horizontal burrow that is considerably con- 

 tracted and bent towards the end in the form of a little cul de sac, which 

 is full of the debris of insects upon which the spider has fed. In one 

 locality this insect debris consisted almost wholly of the remains of Atta 

 barbara, the well known harvesting ant of Palestine and the Mediterra- 

 nean shores. 1 I do not see that the two facts are at all contradictory. 

 The use of the silk lined burrow as a decoy for curious insects in no- 

 wise hinders it from being also useful as a defense against enemies of 

 various sorts. 



One of the most curious examples of relation of structure to enemies, 

 or perhaps of the reaction of hostile environment and agents upon struct- 

 ure is found in a Territelarian spider, Cyclocosmia trun- 

 cata. 2 This aranead, according to Hentz, dwells like 

 others of its kind in cylindrical cavities in the earth. 

 Though many specimens were found, he never saw any 

 lid or closure to the aperture of its dwelling. The very 

 singular formation of its abdomen, which is as hard 

 as leather behind and is truncated to form a perfect 

 circle, induced Hentz to believe that when in danger 

 it closes its dwelling with that part of its body instead 

 of with a trapdoor or lid. This conjecture, of course, 

 needs confirmation, though it seems not im- 

 probable; and one may imagine the intellectual 

 confusion of a pursuing enemy, which finds its 

 prey suddenly disappearing within a hole in 

 the ground, but which, when investigated, pre- 

 sents nothing but a level surface where cer- 

 tainly a hole ought to have been! The dorsal 

 view of the spider is given at Fig. 353 ; the side 

 view at Fig. 354 ; and a diagramatic section 



. _. FIG. 356. Theridium differens, much 



View OI the Creature IS drawn at Fig. 35o, as it enlarged, grasping her cocoon when 



annoyed. FIG. 357. Cocoon nest of 



FIG. 356. 



FIG. 357. 



same. (Natural size.) 



probably would appear when closing up the 

 opening to its burrow. 



Another mode in which enemies may influence the formation of habit 

 in spiders has been suggested by observing the manner in which certain 

 Theridioids defend their cocoons. Theridium differens, a pretty little spi- 

 der inhabiting leaves and foliage (Fig. 357), which makes a flossy round 

 cocoon somewhat larger than itself (about a quarter of an inch in diameter), 

 will grasp her cocoon in her mouth when annoyed by one's finger or by 



1 " Etude sur les Especes de la Famille des Avicularidse," of North Africa. Actes de la 

 Soc. Linn, de Bordeaux, Vol. XLIL, 1888, page 11. 



2 Mygale truncata, Hentz, Spiders U. S., page 16, pi. i., Fig. 1. 



